The present invention relates to volumetric flow measurement, more particularly to measurement of volumetric flow with a transducer interposed in a fluid conduit, which transducer has a rotating rotor from which a signal proportional to flow rate through the transducer is derived, and more particularly to a device for bypassing reverse flow rate pulsations past such a transducer and for time averaging sudden increases and decreases in flow rate through the transducer to overcome inherent response limitations in this particular type of transducer.
A growing concern over long term availability and cost of fuel for automobiles has increased a demand for low-cost fuel flow rate transducers to provide input signals for miles per gallon and total fuel consumption indicating instruments. A flow rate transducer that has a low pressure drop, that provides a wide linear flow rate response range, that provides a digital output signal, and that can be readily incorporated into present automotive fuel supply streams is required for such an application. Fluid flow rate transducers of the turbine type particularly meet these requirements. One such turbine type flow rate transducer is disclosed in U.S. Pat. No. 3,867,840, issued to Wilfried Baatz and assigned to FloScan Instrument Company, expressly incorporated herein by reference. Such turbine type flow rate transducers have a rotor that is rotated at an angular velocity proportional to the steady state fluid flow rate through the transducer. An optical or other electronic sensor is employed to detect the angular velocity of the rotor and to provide an electronic output signal that is proportional to the angular velocity of the rotor.
Such flow rate transducers are capable of providing very accurate output signals over relatively large flow rate ranges when subjected to steady state flow and gradual changes in flow rate. However, automotive fuel supply systems inherently experience abrupt changes in flow rate and moreover never operate under steady state conditions. The flow rate pulsations in an automotive engine fuel supply system are inherently characteristic of the flow generated by a diaphragm pump normally employed to pump fuel from a fuel tank to the carburetor of the engine. The typical diaphragm pump generates flow rate pulsations in the fuel line between the fuel pump and the carburetor that will result in reverse flow of fluid through the line at low average flow conditions. Abrupt flow rate changes also occur under the flow conditions encountered in automotive fuel supply systems. For example, when fuel vapor bubbles present in the fuel supply line vent into the float chamber of a carburetor, a sudden increase in flow rate occurs in the supply line followed by a sudden decrease in flow rate when the vapor bubble is completely vented into the float chamber. Moreover, when the float chamber and float controlled inlet valve in a typical carburetor are moved, the fuel in the float chamber tends to slosh, causing the float controlled inlet valve to open and close quickly, in turn causing abrupt flow rate changes in the fuel line.
The flow rate reversals and the abrupt increases and decreases in flow rate caused by fuel sloshing in the carburetor float chamber and by vapor bubbles in the fuel supply line detrimentally affect the response accuracy of turbine type flow transducers interposed in the fuel supply line. When the transducer is subjected to a continuous series of flow reversals, the fuel flowing backwardly through the transducer will be measured twice in the forward direction causing the turbine type transducer to provide a flow rate signal that is continuously and substantially higher than the average actual flow rate. consequently, the transducer does not provide an accurate signal for indicating actual flow rate or for calculating total flow through the transducer. When the transducer rotor is subjected to a sudden increase in flow rate followed by a sudden decrease in flow rate, the rotor will tend to speed up more quickly in response to the increase in flow rate than it will tend to slow down after a corresponding decrease in flow rate. Thus, integration of the flow rate signal with respect to time will provide an indication of total flow that is greater than the actual flow through the transducer.
Although one skilled in the electronic signal conditioning art can define an electronic circuit that will compensate for the signal error derived from the turbine type transducer under these flow conditions, such an electronic circuit would be relatively sophisticated and expensive to produce. For some application, the electronic approach to solving the problem might be applicable. However, for use in conjunction with an automobile fuel system, an electronic signal conditioning circuit for eliminating the error from the indicated signal would be relatively expensive, and would prohibit its use, even on a large mass production scale.
It is therefore an object of the present invention to provide a flow rate transducer system that can provide an accurate indication of flow rate and total fluid flow without the necessity of electronically conditioning the signal to eliminate error. It is a further object of the present invention to provide a relatively inexpensive, mechanical device that can be employed in a fluid flow measurement system to adjust the flow through a turbine type transducer so that the signal from the transducer is indicative of the actual average flow rate through the fluid system. It is a further object of the present invention to provide a device that bypasses fluid flow rate pulsations that result in flow reversals past the flow transducer while averaging all fluid flow through the transducer. It is a further object of the present invention to provide such a device that isolates the flow transducer from sudden increases or decreases in flow rate. It is another object of the present invention to provide such a device that averages the flow through the transducer over a period of time so as to eliminate flow rate pulsations through the transducer. It is still another object of the present invention to provide such a device that is relatively simple in concept, economical to manufacture, easy to install in present fluid flow systems and is easy and inexpensive to maintain. It is also an object of the present invention to provide an improvement in such a device that aids in eliminating flow discontinuities through the flow rate transducer caused by vapor bubbles present in a liquid as it passes through the flow rate transducer. It is still another object of the present invention to provide a device that accomplishes the foregoing objects while providing a means for cooling the fuel passing through the transducer to decrease the volume of vapor production in the fuel line.